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Viscoelastic processes associated with the glass‐rubber transition of an amorphous polymer are considered to involve hindered rotations around main‐chain bonds, which give rise to a decrease in molecular distortion in the stressed material and to an orientation or disorientation of chain segments. The local distortional changes are associated with variations in energy‐elastic stress. The orientational rearrangements yield changes in conformational entropy and energy and may be described in the long‐time region by the normal mode motions of Gaussian submolecules. Assuming that the net time‐dependent stress and birefringence may each be expressed as the sum of distortional and orientational contributions, methods are proposed on the basis of stress‐optical data for resolving the distortional and orientational stresses or moduli during stress‐relaxation, creep, and dynamic mechanical tests. An analysis of dynamic birefringence data for different amorphous polymers indicates that the orientational processes become important in the long relaxation‐time region and are consistent with predictions of the submolecular theory. The distortional changes dominate the shorter relaxation‐time behavior and are characterized by somewhat narrower distributions of relaxation times than are apparent from the unresolved data.

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The phenomenon of selective adsorption exhibited by macromolecules in mixed solvents is discussed in terms of the lattice model theory of polymer solutions. Application of this treatment to some light-scattering data on the system benzene+ cyclohexane + polystyrene indicates that a ternary interaction parameter ~1 2 3 , which is not found in any two-component mixture, is required to fit the results.

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